Adam Lanza in a 2008 school yearbook from Newtown High School Photo: Splash News

The gunman in the Connecticut shooting rampage shot his mother four times in the head before going to the school and gunning down 26, authorities said Sunday as details emerged suggesting that Adam Lanza had planned an even more gruesome massacre but was stopped short.

Lanza blasted his way into the building and used a high-powered rifle to kill 20 children and six adults, including the principal who tried to stop him, authorities said.

The unthinkable bloodshed might even have been worse. Gov. Dannel Malloy said Lanza shot himself when he heard police coming. Authorities said they found multiple 30-round magazines and hundreds of bullets at the school, enough ammunition on him to carry out significant additional carnage.

“There was a lot of ammo, a lot of clips,” State Police Lt. Paul Vance. “Certainly a lot of lives were potentially saved.”

“He used a weapon to open up the glass and then walked in,” he said. “He discharged to make an opening and then went through it, went to the first classroom, as you know, went to the second classroom.”

“We surmise that it was during the second classroom episode that he heard responders coming and apparently at that, decided to take his own life,” Malloy said.

Malloy offered no possible motive for the shooting and a law enforcement official has said police have found no letters or diaries left behind that could shed light on it.

The shooting is the largest massacre of school-age children in U.S. history.

Later this morning, Connecticut state police Lt. Paul Vance told members of the media he was “confident” that police will be able to “answer every question possible” after their investigation is complete.

He added that the bodies of the victims are already being released to their parents.

A funeral for one of the children, 6-year-old Noah Pozner, is being planned for Monday.

Vance also said he hopes the Connecticut state police will be able to provide full information later this afternoon on the last two fatal victims of Adam’s rampage, noting that the shooter had four firearms with him, one more than the number of weapons he was originally believed to have.

Newtown police Lt. George Sinko said that school officials will determine what happens but that he thinks it will be very difficult for the children to return to Sandy Hook Elementary in Newtown.

But he says authorities want to keep the children together because the survivors “need to support each other.”

Vance also took a harsh tone towards people pretending to be the shooter or otherwise spreading misinformation, including threatening and inaccurate details, about the case on social media.

Anyone perpetrating misinformation on social media “could be arrested and prosecuted under federal law,” Vance said.

Meanwhile, two senators called Sunday for a national commission to examine mass shootings in the United States, while a third vowed to ban the sale of military-style assault weapons.

The proposals were among the first to come from Congress in the wake of Friday’s school shooting in Newtown, Conn. Gun rights activists remained largely quiet on the issue, all but one declining to appear on the Sunday talk shows. Meanwhile, Democrats vowed action and said it was time to hear from voters — not gun lobbyists — on how to prevent the next shooting.

The time for “saying that we can’t talk about the policy implications of tragedies like this is over,” said Rep. Chris Murphy, D-Conn., who won a Senate seat in the November elections.

President Barack Obama and Senate Democrats haven’t pushed for new gun controls since rising to power in the 2008 national elections. Outspoken advocates for stricter laws, including Sen. Dianne Feinstein, say that’s because of the powerful sway of the National Rifle Association.

But advocates also say the latest shooting is a tipping point that could change the dynamic of the debate dramatically. Feinstein, D-Calif., said she plans to create a national committee devoted to rallying support for a ban on the sale of new assault weapons and will propose legislation next year that would ban big clips, drum and strips of more than 10 bullets.

“It can be done,” she said Sunday of reviving the 10-year ban that expired in 2004.

Sen. Joseph Lieberman, an independent from Connecticut who is retiring, said there should be a national commission to scrutinize gun laws and loopholes, as well as the nation’s mental health system and the role that violent video games and movies might play in shootings. Senate Democratic Whip Dick Durbin of Illinois said he would support such a panel, adding that it was time for a “national discussion” that included school safety.

“This conversation has been dominated in Washington by — you know and I know — gun lobbies that have an agenda” Durbin said. “We need people, just ordinary Americans, to come together, and speak out, and to sit down and calmly reflect on how far we go.”

Congress has frequently turned to independent bipartisan commissions to try to solve the nation’s worst problems, including the 9/11 terrorist attacks, the Iraq war and the failing economy. But ultimately, lawmakers are often reluctant to act on the recommendations of outsiders, especially if they think it will cost them support in their home states.

Still, Lieberman defended the idea of a national commission as the only way to ensure that the “heartbreak and anger” of the Connecticut shooting doesn’t dissipate over time and that other factors beyond gun control are considered.

“We’ve got to continue to hear the screams of these children and see their blood until we do something to try to prevent this from happening again,” he said.

Gun rights advocates appeared reluctant to make their case against tougher gun laws while Connecticut families and the nation were still in the earliest stages of grieving. David Gregory, the host of “Meet the Press,” said NBC invited all 31 “pro-gun” senators to appear on Sunday’s show, and all 31 declined. All eight Republicans on the Senate Judiciary Committee were unavailable or unwilling to appear on CBS’ “Face the Nation,” host Bob Schieffer said.

Rep. Louie Gohmert, R-Texas, was the sole representative of gun rights’ activists on the various Sunday talk shows. In an interview on “Fox News Sunday,” Gohmert defended the sale of assault weapons and said that the principal at Sandy Hook Elementary School, who authorities say died trying to overtake the shooter, should herself have been armed.

“I wish to God she had had an M-4 in her office, locked up so when she heard gunfire, she pulls it out and she didn’t have to lunge heroically with nothing in her hands. But she takes him (the shooter) out, takes his head off before he can kill those precious kids,” Gohmert said.

Gohmert also argued that violence is lower in cities with lax gun laws, and higher in cities with stricter laws.

“The facts are that every time guns have been allowed —conceal-carry (gun laws) have been allowed — the crime rate has gone down,” Gohmert said.

Gun control advocates say that isn’t true. A study by the California-based Law Center to Prevent Gun Violence determined that seven of the 10 states with the strongest gun laws — including Connecticut, Massachusetts and California — are also among the 10 states with the lowest gun death rates.

“If you look at the states with the strongest gun laws in the country, they have some of the lowest gun death rates, and some of the states with the weakest gun laws have some of the highest gun death rates,” said Brian Malte of the Brady Campaign to Prevent Gun Violence.

In an interview that aired Sunday on NBC’s “Meet the Press,” Mayor Bloomberg said the kind of violence resulting in the deaths of 20 schoolchildren “only happens in America.” And he says it happens “again and again.”

Bloomberg has been an outspoken gun control advocate for years. He noted that New York state has some of the toughest gun laws in the country, and New York City the lowest murder rate of any big American city.

The mayor says it’s time for the president to stand up and tell the country what needs to happen — not go to Congress and ask what legislators want to do.

President Obama will visit Newtown tonight to meet with families of the victims and speak at a vigil.

Yesterday, it was revealed that Adam’s mother took her shy son to shooting ranges.

“She’d take them to the range a lot . . . Nancy was an enthusiast — so much so that she wanted to pass it on to her kids,” said her former landscaper and occasional drinking buddy Dan Holmes.

Adam tried to buy a rifle three days before the attack from a Dick’s Sporting Goods store in Danbury, Conn., but was turned away, employees confirmed.

The madman was rebuffed because he refused to follow the mandatory waiting period or undergo a background check, NBC News reported.

Officials were also investigating whether Adam had an “altercation” with four school employees the day before the killings, NBC reported.

The victims of the slaughter were killed at close range by rifle shots, according to the state’s chief medical examiner.

“Everybody was hit more than once,” said Dr. H. Wayne Carver at a news conference yesterday afternoon outside the school.

He said that the seven victims he personally examined suffered between three and 11 gunshot wounds.

Carver said the bullets used by the cold-blooded killer were designed specifically to penetrate deep tissue and do a “devastating” amount of damage.

All the deaths are classified as homicides, said Carver, who described the scene as the worst that he’s seen in his 30-year career.

The victims — dressed in “cute kid stuff” — suffered a “very devastating set of injuries,’’ he said.

Last night, the killer’s family released their first statement on the tragedy, saying: “Our family is grieving along with all those who have been affected . . . We too are asking why. We have cooperated fully with law enforcement.”